1. Field of Invention
The present invention relates to loudspeakers and more particularly to a loudspeaker surround design that maximizes the cone diameter without the necessity of changing the outer dimensions of the loudspeaker frame.
2. Related Art
The general construction of a loudspeaker driver consists of a diaphragm, voice coil, magnetic motor, frame and suspension system. The magnetic motor is generally attached to the frame. The voice coil and diaphragm are then mounted to the frame via the suspension system, which may include one or more suspension members. The voice coil of the driver typically consists of a voice coil former having a wire wound about the lower portion of the voice coil former. Often times, although not necessary, the voice coil former is encased in a wrapper. The suspension system of the driver acts to provide the stiffness of the driver and also provide air sealing for the driver. The configuration of the voice coil and diaphragm in the frame via the suspension system depends generally upon the design and size of the diaphragm relative to the voice coil.
Prior Art FIG. 1 illustrates the construction of a typically conventional dual-suspension driver and the typically connection of the surround to the frame and diaphragm. As seen in FIG. 1, the loudspeaker driver 100 consists of a diaphragm 102, voice coil 104, magnetic motor 106, frame 108 and suspension system, which consists of both a surround 110 and a spider 112. In a conventional dual-suspension driver 100, the diaphragm 102 of the driver 100 is formed as a cone and is substantially greater in diameter than that of the voice coil 104. In this type of construction, two suspension members are generally utilized. A “surround” suspension member 110 is connected to the diaphragm 102 at its outer edge and extends outward from the diaphragm 102 to connect the diaphragm 102 to the frame 108. Similarly, a “spider” suspension 112 is connected to the voice coil 104 and extends from the voice coil 104 to the frame 108, connecting the voice coil 104 to the frame 104.
Prior Art FIG. 2 in an enlarged view of the encircled portion of FIG. 1 and illustrates the typical connection of the diaphragm 102 to the frame 108 via the surround 110. As seen in FIG. 2, the frame 108 includes an outer mounting ring 114, which includes a rim 116 and a general flat landing section 118. The rim 116 includes both an inner wall 120 and outer wall 122. A typical surround 110 has a central portion 124 that is generally half-circular or arched in shape. A radial planar exterior flange 126 extends about the outer diameter of the central arched portion 124 of the surround 110 for adhesive attachment to the landing section 118 of the outer mounting ring 114 of the frame 108. A radial planar interior flange 128 extends about the inner diameter of the central arched portion 124 of the surround 110. This radial planar interior flange 128 is designed for the adhesive attachment of the interior flange 128 to the diaphragm 102. The central arched portion 124 of the surround 110 is a flexible portion of the surround 110 and functions to constrain the diaphragm 102 radially yet allows it to vibrate in an axial direction when driven by the voice coil 104.
Prior Art FIG. 2 illustrates the position of the diaphragm and its surround in solid lines for the normal “at rest” condition. The displaced position of surround and diaphragm are shown in dashed lines for a maximum driven condition at maximum downward cone excursion. Displacement of the central arched portion of the surround provides an effective piston diameter that is somewhat larger than the cone diameter extending to a mid-region of the central arched portion.
Because of the need to provide adequate area to secure the diaphragm to the frame, as illustrated in prior art FIGS. 1 and 2, a large amount of diameter area, relative to the overall footprint or outside diameter of the loudspeaker, often is sacrificed. In certain applications, such as vehicular loudspeakers, the decreased diameter of the diaphragm relative to the overall speaker diameter can restrict the loudspeakers ability to operate at lower frequencies and thus achieve higher efficiency levels.
The area of a diaphragm is a major contributing factor to a loudspeaker's efficiency because as the size of a diaphragm of a loudspeaker becomes smaller, achieving acceptable low frequency response becomes more difficult. To achieve lower frequency responses, a loudspeaker is required to displace larger volumes of air, and the suspension stiffness must be reduced to maintain a low resonance corresponding to the lighter mass of the smaller driver. The volume of air that a loudspeaker can displace is dependent upon the area of the diaphragm and the range of motion allowed by the suspension, i.e., amount of vibrational excursion, or volume displacement, of the loudspeaker.
Large quantities of small-sized loudspeakers are used in vehicles such as cars, trucks, boats, aircraft, and etc. Loudspeaker for use in vehicles are generally designed to mechanically fit a particular mounting pattern used by vehicle manufacturers, which typically includes a main cutout and surrounding mounting holes, dimensioned according to standards originating from different world regions. Original, as well as, replacement speakers are generally required to fit the mounting pattern and space originally provided in the vehicle. As such, the outer dimensions of the frame of the loudspeaker generally must meet these predefined dimensions.
Because the size of the loudspeaker for use in vehicles is predefined, the area of the diaphragm of each loudspeaker is also thereby limited. While it would be very simple to increase the efficiency by increasing the size of the speaker diameter, if the frame diameter or any of its critical dimensions were changed, the loudspeaker would cease to become a standard sized loudspeaker and its application would thereby be limited. Small-sized or compact loudspeakers for use in vehicles are typically categorized according to the dimensions of the loudspeaker frames and are commonly found in the following nominal sizes—4 inch, 5¼ inch and 6½ inches.
Round speakers having basket diameter in the 4″-7″ size range are manufactured in extremely high quantities for vehicular usage in the United States and throughout the world. Most of loudspeakers in the 6″-7″ range are made to either a JIS Japanese standard that specifies 6.18 inches (157 mm) diameter or a DIN German standard used in Europe that specifies 6.69 inches (170 mm) diameter.
With the typically surround mounting construction described above, the area of the diaphragm is generally less that than that of the overall speaker size. Since the area of the diaphragm is a key factor in the efficiency of the loudspeaker, a useful factor of merit regarding size efficiency of a loudspeaker may be obtained by comparing the cone or diaphragm area to the total projected frame area. Table 1 below illustrates the diaphragm diameter, frame diameter, and the ratio between the diaphragm area and the frame area for typical loudspeaker sizes of the construction ascribed above.
TABLE 1KEY DIMEN SIONS IN POPULAR COMPACT SPEAKERSRATIO OFCONEFRAMECONE AREA/NOMINALDIAMETERDIAMETERFRAMESIZEVERSION(MM)(MM)AREA   4 inch73102.30.515¼ inch921290.516½ inchJIS Japan (a)111.81570.51      (b)115.31570.54DIN Europe119.31700.49
TABLE 1 shows that a conventional speaker structure typically provides a ratio of cone/basket area=0.51. The (b) version of the JIS type represents an effort to upgrade part way toward the DIN cone size and corresponding midrange and low frequency performance capability while retaining the smaller JIS basket size.
Practical all loudspeakers are subject to an inherent dropout of acoustic efficiency at a low-end cutoff frequency in inverse proportion to the diaphragm area (for a given cone excursion). Thus, for full range speakers of any size, it is very beneficial to increase the cone diameter. Each percent that the cone diameter can be increased yields more than double the percent increase in diaphragm area. Accomplishing increased diaphragm area without increasing the outer dimensions of the speaker frame, whether the frame and diaphragm are round, oval or other shape, is particularly beneficial to midrange and low frequency performance of compact speakers that are subject to strict constraints on frame size, such as those used in vehicular sound systems as well as in small personal radio/stereo players, multi-media computer systems, etc.
A need therefore exists for mounting for the surround to the frame of the loudspeaker in a manner that would enable the use of larger conventional diaphragm sizes in frames having strict size constraints and accordingly enhance the midrange and low frequency performance of the loudspeakers.